Thermally Driven Lanthanide Dual‐Site Doping Enables High Performance Perovksite Solar Cells via Halide Migration Suppression

Wide‐bandgap (WBG) perovskite solar cells (PSCs) are critical for tandem architectures but suffer from light‐induced halide segregation and non‐radiative recombination. Although conventional rare‐earth doping passivates defects, it concurrently introduces vacancies and lattice strain that exacerbate halogen migration. Herein, we report a thermally induced doping strategy where Pr 3+ /Sm 3+ ions pre‐embedded in MeO‐4PACz diffuse into the perovskite during annealing. Through combined tolerance factor analysis, structural characterization, and DFT calculations, we identify a dual doping mechanism: predominant interstitial incorporation with minor B‐site substitution. This approach reduces defect density, increases iodine migration energy barriers (from 0.85 to 0.94 and 1.12 eV), and minimizes lattice distortion. Consequently, the experimental results show that the open‐circuit voltage increases from 1.198 V to 1.230 V (Pr 3+ ) and 1.233 V (Sm 3+ ), and the fill factor increases from 83% to 86%. Finally, the PCE reached 23.04% (Pr 3+ ) and 23.39% (Sm 3+ ) (20.12% for control) with > 90% stability retention after 1500 h. In addition, the optimized semitransparent WBG device PCE was 19.48% (Pr 3+ ) and 19.85% (Sm 3+ ), and the PCE of 4‐T perovskite was 27.05% (Pr 3+ ) and 27.56% (Sm 3+ ). This method will be beneficial for the development and application of WBG PSCs and TSCs.